The Q&A Archives: Seedling fungal disease

Question: For my garden this year, I have started about 20 different plants under grow lights in my basement. They were all doing well until the mushrooms started popping up, closely followed by a white wispy fungus covering the soil. Both the containers and germinating mix I used were sterile, so I know that isn't the problem. Could the soil be too wet, and if that's the case, what should I do about it? If not, can I do anything at all? Only one plant flat has shown any ill effects because of it. One tomato flat has developed black spots on some of its leaves, followed by the leaves falling off. Some leaves on the plants also fell off by themselves. When I noticed this, I immediately moved it upstairs away from the other plants. Is there anything I can do to save the plant, or is there even a problem?

Answer: Oh yeah, unfortunately, this is a problem. If you had mushrooms sprouting in your soil, it was not sterile to begin with. If you purchased it, I would return any leftovers and ask for a refund. Sterile soil should not contain mushroom spores. Sterile soil also would not contain the organisms that result in the black spots on your tomatoes. What about the containers you are growing in? Are you absolutely positive they were sterile? Sterilize them by washing first in soapy water and then, rinse in a solution of 1 part bleach to 10 parts water and allow to air dry. It does sound like your soil may have been too wet as well. Keep an eye on watering, don't let your soil dry out but never let it get to the point it could be considered "wet" either. What about the air circulation in the basement? Seedlings need very good air circulation to head off fungal diseases. Consider placing a fan in the basement, not directly on the seedlings but enough wind to stir the air up a bit. Also, the cool temperatures and dampness in most basements can stress and stunt seedlings, inviting problems. I would start some more tomatoes and try to improve the situation for the other seedlings using the above suggestions.

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